Physical Properties of pH-sensitive Quaternary Pyridinium Salt Incorporated Acrylic Resin

Objectives: The Quaternary Pyridinium Salt (QPS) can selectively inhibit growth of acid-producing bacteria in a biofilm community and maintain a stable oral environment. This study tested the effects of pH-sensitive QPS incorporation on the physical properties of polymethyl methacrylate (PMMA) orthodontic/denture acrylic resin material.

Methods: Samples were prepared with incorporation of different concentrations (0%-control, 5%, 10%, 15%, and 20%) of QPS into the PMMA resin (Great Lakes Biocryl, USA). The mixed samples were placed into a pressure cooker for polymerization and polished. Three physical property tests were conducted: Vickers surface hardness, water sorption, and water solubility. For surface hardness, seven disks (10x2mm) were used for each group. Samples were soaked in water at 37C for 24 hours before the readings. Vickers hardness values were calculated and then averaged among the three values. For water sorption tests, fifteen samples were used for each group. The volume of each sample was measured. Samples were then kept at room temperature for 30 minutes and were immediately weighed (M1). The samples were placed into a deionized water at 37C and weighed every 24 hours until a constant weight (M2) was achieved. The samples were then dried out for water solubility measurements and weighed daily until constant weight was achieved for weight (M3). The values for water sorption and water solubility were calculated. The data was evaluated using One–way ANOVA and Tukey tests.

Results: For the surface hardness, no significant differences were found between control, 5%, 10%, 15%, and 20% test groups (p>0.05). Both water sorption and solubility values also showed no significant difference between control, 5%, 10%, 15%, and 20% groups as well (p>0.05).

Conclusions: Incorporation of QPS into PMMA did not change the tested physical properties of resin material. Therefore, this incorporation should be microbiologically tested in terms of bacterial accumulation.